In recent years, accompanying the increase in the number of diabetics, the self monitoring of blood glucose monitoring daily movements in blood sugar level by the patient himself has come to be recommended.
The measurement of blood sugar level is carried out by use of a blood glucose monitoring apparatus for automatically measuring the amount of glucose in blood. Prior to the measurement, the patient must sample his own blood.
A method of sampling blood includes the steps of puncturing the skin of a fingertip by a lancet and then pressing the vicinity of the puncture portion with fingers or the like to squeeze out the blood.
The puncture of a fingertip with a lancet is conducted by use of a lancet instrument (refer to, for example, U.S. Pat. No. 6,540,762) having a lancet and a casing (cap) storing the lancet movably therein. Specifically, the lancet instrument is fitted to the lancing apparatus, and the lancing apparatus is operated to project the lancet, thereby puncturing a fingertip.
In addition, after the puncture (after the use), the lancet instrument in the condition where the lancet tip is located in the casing has the lancet and the casing engaged with each other by friction between the outer periphery of a hub (lancet hub) provided on the lancet and the inner periphery of the casing. This ensures that the lancet tip, after the puncture, can be prevented from projecting through the opening (tip opening) of the casing.
However, in the lancet instrument thus configured, the engagement between the lancet and the casing may be weakened (due to a decrease of the frictional force) due, for example, to vibration or the like, and the lancet may be moved (displaced) toward the opening side, i.e., the lancet tip may project from the opening.
Besides, in the case where the lancet tip of the lancet instrument after the puncture (after the use) projects from the opening, the patient's skin or the like, for example, may be injured by mistake.